CDM8 based CSI-RS designs for MIMO

ABSTRACT

A network node, wireless device, base station, user equipment and corresponding methods are provided. The network node includes processing circuitry configured to: select a first set and second set of reference signal resources in a subframe and aggregate the first set and second set of reference signal resources in the subframe to form a code division multiplexing, CDM, aggregation configuration. The first set and second set of reference signal resources in the subframe satisfy a temporal criterion such that any two resource elements in the first set and second set of reference signal resources have up to a maximum time separation of six OFDM symbols. The first set and second set of reference signal resources in the subframe satisfy a frequency criterion such that any two resource elements in the first set and second set of reference signal resources have up to a maximum frequency separation of six subcarriers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of patent application Ser. No.16/352,433, filed Mar. 13, 2019 and claims priority to U.S. patentapplication Ser. No. 15/764,062, filed Mar. 28, 2018 (now U.S. patentSer. No. 10/931,418) entitled “CDM8 BASED CSI-RS DESIGNS FOR MIMO,”which claims priority to International Application No.:PCT/IB2017/056048, filed Sep. 30, 2017 entitled “CDM8 BASED CSI-RSDESIGNS FOR MIMO,” which claims priority to U.S. Provisional PatentApplication No. 62/403,044 filed Sep. 30, 2016 entitled “CDM8 BASEDCSI-RS DESIGNS FOR MIMO,” the entireties of all of which areincorporated herein by reference.

TECHNICAL FIELD

Wireless communications, and in particular to code divisionmultiplexing, CDM, aggregation configurations for reducing performancelosses due to channel variations in wireless communications.

BACKGROUND

Long Term Evolution (LTE) uses Orthogonal Frequency DivisionMultiplexing (OFDM) in the downlink and Discrete Fourier Transform(DFT)-spread OFDM in the uplink. The basic LTE downlink physicalresource can thus be seen as a time-frequency grid as illustrated inFIG. 1 , where each resource element corresponds to one OFDM subcarrierduring one OFDM symbol interval. Further, as shown in FIG. 2 , in thetime domain, LTE downlink transmissions are organized into radio framesof 10 ms, each radio frame consisting of ten equally-sized subframes oflength Tsubframe=1 ms.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and 12 contiguous subcarriers in thefrequency domain. Resource blocks are numbered in the frequency domain,starting with 0 from one end of the system bandwidth. Downlinktransmissions are dynamically scheduled, i.e., in each subframe thenetwork node transmits control information about to which terminals datais transmitted and upon which resource blocks the data is transmitted,in the current downlink subframe. This control signaling is typicallytransmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. Adownlink system with 3 OFDM symbols as control is illustrated in FIG. 3, which illustrates s downlink subframe.

Codebook-Based Precoding

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance isparticularly improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO. The LTE standard iscurrently evolving with enhanced MIMO support. A core component in LTEis the support of MIMO antenna deployments and MIMO related techniques.Currently, LTE-Advanced supports an 8-layer spatial multiplexing modefor 8 Tx antenna ports with channel dependent precoding. LTE-AdvancedPro adds 8-layer spatial multiplexing support for 2D (2 dimensional)/1D(1 dimensional) port layouts with 8/12/16 Tx antenna ports with channeldependent precoding. In LTE Release 14, support for 8-layer spatialmultiplexing for 2D/1D port layouts with 20/24/28/32 Tx antenna ports isbeing specified. The spatial multiplexing mode is aimed for high datarates in favorable channel conditions. An illustration of the spatialmultiplexing operation is provided in FIG. 4 , which illustrates atransmission structure of precoded spatial multiplexing mode in LTE.

As seen in FIG. 4 , the information carrying symbol vector s ismultiplied by an N_(T)×r precoder matrix W, which serves to distributethe transmit energy in a subspace of the N_(T) (corresponding to N_(T)antenna ports) dimensional vector space. The precoder matrix istypically selected from a codebook of possible precoder matrices, andtypically indicated by means of a precoder matrix indicator (PMI), whichspecifies a unique precoder matrix in the codebook for a given number ofsymbol streams. The r symbols in s each correspond to a layer and r isreferred to as the transmission rank. In this way, spatial multiplexingis achieved since multiple symbols can be transmitted simultaneouslyover the same time/frequency resource element (TFRE). The number ofsymbols r is typically adapted to suit the current channel properties.

LTE uses OFDM in the downlink (and DFT precoded OFDM in the uplink) andhence the received N_(R)×1 vector y_(n) for a certain TFRE on subcarriern (or alternatively data TFRE number n) is thus modeled byy _(n) =H _(n) Ws _(n) +e _(n)  Equation 1

where e_(n) is a noise/interference vector. The precoder W can be awideband precoder, which is constant over frequency, or frequencyselective.

The precoder matrix is often chosen to match the characteristics of theN_(R)×N_(T) MIMO channel matrix H_(n), resulting in so-called channeldependent precoding. This is also commonly referred to as closed-loopprecoding and essentially strives for focusing the transmit energy intoa subspace which is strong in the sense of conveying much of thetransmitted energy to the UE. In addition, the precoder matrix may alsobe selected to strive for orthogonalizing the channel, meaning thatafter proper linear equalization at the UE, the inter-layer interferenceis reduced.

The transmission rank, and thus the number of spatially multiplexedlayers, is reflected in the number of columns of the precoder. Forefficient performance, it is important that a transmission rank thatmatches the channel properties is selected.

2D Antenna Arrays

Developments in Third Generation Partnership Project (3GPP) has led tothe discussion of two-dimensional antenna arrays where each antennaelement has an independent phase and amplitude control, thereby enablingbeamforming in both in the vertical and the horizontal dimensions. Suchantenna arrays may be (partly) described by the number of antennacolumns corresponding to the horizontal dimension N_(h), the number ofantenna rows corresponding to the vertical dimension N_(v), and thenumber of dimensions corresponding to different polarizations N_(p). Thetotal number of antenna elements is thus N=N_(h)N_(v)N_(p). An exampleof an antenna where N_(h)=8 and N_(v)=4 is illustrated in FIG. 5 below.It furthermore consists of cross-polarized antenna elements meaning thatN_(p)=2. We will denote such an antenna as an 8×4 antenna array withcross-polarized antenna elements.

However, from a standardization perspective, the actual number ofelements in the antenna array is not visible to the wireless device, butrather the antenna ports, where each port corresponds to a CSI (channelstate information) reference signal described further below. Thewireless device can thus measure the channel from each of these ports.Therefore, a 2D port layout is introduced, described by the number ofantenna ports in the horizontal dimension M_(h), the number of antennarows corresponding to the vertical dimension M_(v) and the number ofdimensions corresponding to different polarizations M_(p). The totalnumber of antenna ports is thus M=M_(h)M_(v)M_(p). The mapping of theseports on to the N antenna elements is an eNB implementation issue andthus not visible to the wireless device. The wireless device does noteven know the value of N; it only knows the value of the number of portsM.

For LTE Rel-12 wireless device and earlier, only a codebook feedback fora 1D port layout is supported, with 2,4 or 8 antenna ports. Hence, thecodebook is designed assuming these ports are arranged on a straightline. In LTE Rel-13, codebooks for 2D port layouts were specified forthe case of 8, 12, or 16 antenna ports. In addition, a codebook 1D portlayout for the case of 16 antenna ports was also specified in LTERel-13. The specified Rel-13 codebooks for the 2D port layouts can beinterpreted as a combination of precoders tailored for a horizontalarray and a vertical array of antenna ports. This means that (at leastpart of) the precoder can be described as a function of

$\begin{matrix}{v_{l,m} = \begin{bmatrix}u_{m} & {e^{j\frac{2\pi l}{O_{1}N_{1}}}u_{m}} & \ldots & {e^{j\frac{2\pi{l({N_{1} - 1})}}{O_{1}N_{1}}}u_{m}}\end{bmatrix}^{T}} & {{Equation}2}\end{matrix}$ wherein $\begin{matrix}{u_{m} = \begin{bmatrix}1 & e^{j\frac{2\pi m}{O_{2}N_{2}}} & \ldots & e^{j\frac{2\pi{m({N_{2} - 1})}}{O_{2}N_{2}}}\end{bmatrix}} & {{Equation}3}\end{matrix}$

In Equation 2-Equation 3, the parameters N₁ and N₂ denote the number ofports in the 1^(st) dimension and the 2^(nd) dimension, respectively.For 1D port layouts, N₂=1 and u_(m) in equation 3 becomes 1. It shouldbe noted that the 1^(st) dimension could either be the horizontaldimension or the vertical dimension and the 2^(nd) dimension wouldrepresent the other dimension. In other words, using the notation ofFIG. 5 , two possibilities: (1) N₁=M_(h) and N₂=M_(v), (2) N₁=M_(v) andN₂=M_(h) could exist, where FIG. 5 illustrates a two-dimensional antennaarray of cross-polarized antenna elements (N_(p)=2), with N_(h)=4horizontal antenna elements and N_(v)=8 vertical antenna elements, andin the right hand side of FIG. 5 , the actual port layout with 2vertical ports and 4 horizontal ports. This could for instance beobtained by virtualizing each port by 4 vertical antenna elements.Hence, assuming cross-polarized ports are present, the wireless devicewill measure 16 antenna ports in this example.

The O₁ and O₂ parameters in Equation 2-Equation 3 represent the beamspatial oversampling factors in dimensions 1 and 2, respectively. Thevalues of N₁, N₂, O₁ and O₂ are configured by radio resource control(RRC) signaling. The supported configurations of (O₁,O₂) and (N₁,N₂) fora given number of CSI-RS ports are given in Table 7.2.4-17 of 3GPP TS36.213 Technical Specification Group Radio Access Network, EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical layer procedures(Release 13); V13.0.1 (2016 January), which is reproduced below in Table1.

Number of CSI-RS antenna ports (N₁, N₂) (O₁, O₂) 8 (2, 2) (4, 4), (8, 8)12 (2, 3) (8, 4), (8, 8) (3, 2) (8, 4), (4, 4) 16 (2, 4) (8, 4), (8, 8)(4, 2) (8, 4), (4, 4) (8, 1) (4, -), (8, -)

Table 1. Supported configurations of (O₁,O₂) and (N₁,N₂) Table 7.2.4-17of 3GPP TS 36.213 Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layerprocedures (Release 13); V13.0.1 (2016 January).

The details of the LTE Rel-13 codebooks defined using the quantity inEquation 2 can be found in Tables 7.2.4-10, 7.2.4-11, 7.2.4-12,7.2.4-13, 7.2.4-14, 7.2.4-15, 7.2.4-16, and 7.2.4-17 of 3GPP TS 36.213.

Non-Zero Power Channel State Information Reference Symbols (NZP CSI-RS)

In LTE Release-10, a new reference symbol sequence was introduced forthe intent to estimate channel state information, the NZP CSI-RS. TheNZP CSI-RS provides several advantages over basing the CSI feedback onthe cell-specific reference symbols (CRS) which were used, for thatpurpose, in previous releases. Firstly, the NZP CSI-RS is not used fordemodulation of the data signal, and thus does not require the samedensity (i.e., the overhead of the NZP CSI-RS is substantially less).Secondly, NZP CSI-RS provides a much more flexible means to configureCSI feedback measurements (e.g., which NZP CSI-RS resource to measure oncan be configured in a wireless device specific manner).

By measuring on a NZP CSI-RS, a wireless device can estimate theeffective channel the NZP CSI-RS is traversing including the radiopropagation channel and antenna gains. In more mathematical rigor thisimplies that if a known NZP CSI-RS signal x is transmitted, a wirelessdevice can estimate the coupling between the transmitted signal and thereceived signal (i.e., the effective channel). Hence if novirtualization is performed in the transmission, the received signal ycan be expressed asy=Hx+e  Equation 4

and the wireless device can estimate the effective channel H. Up toeight NZP CSI-RS ports can be configured for a LTE Rel.11 wirelessdevice, that is, the wireless device can thus estimate the channel fromup to eight transmit antenna ports in LTE Rel-11.

Up to LTE Rel-12, the NZP CSI-RS utilizes an orthogonal cover code (OCC)of length two to overlay two antenna ports on two consecutive REs. Alength-2 OCC can be realized by the pair of orthogonal codes [1 1] and[1 −1]. Throughout this document, OCC is alternatively referred to ascode division multiplexing (CDM). A length-N OCC may be either referredto as OCC-N or as CDM-N where N can take on values of 2, 4, or 8.

As seen in FIG. 6 , many different NZP CSI-RS patterns are available, inwhich FIG. 6 illustrates resource element grid over an RB pair showingpotential positions for UE specific RS (distinguished by respectivehatching(s)), CSI-RS (marked with a number corresponding to the CSI-RSantenna port), and CRS (distinguished by respective hatching(s)) as iswell known in the art. For the case of 2 CSI-RS antenna ports, there are20 different patterns within a subframe. The corresponding number ofpatterns is 10 and 5 for 4 and 8 CSI-RS antenna ports, respectively. ForTime Division Duplex (TDD), some additional CSI-RS patterns areavailable.

The reference-signal sequence for CSI-RS is defined in Section 6.10.5.1of 3GPP TS 36.211 Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channelsand modulation (Release 13); V13.0.0 (2015 December) as

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots,{N_{RB}^{\max,{DL}} - 1}} & {{Equation}5}\end{matrix}$where n_(s) is the slot number within a radio frame and l is the OFDMsymbol number within the slot. The pseudo-random sequence c(i) isgenerated and initialized according to Sections 7.2 and 6.10.5.1 of [2]3GPP TS 36.211 Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channelsand modulation (Release 13); V13.0.0 (2015 December), respectively.Furthermore, in Equation 5, N_(RB) ^(max,DL)=110 RB is the largestdownlink bandwidth configuration supported by specification 3GPP TS36.211 Technical Specification Group Radio Access Network, EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical channels andmodulation (Release 13); V13.0.0 (2015 December).

In LTE Rel-13, the NZP CSI-RS resource is extended to include 12 and 16ports. Such Rel-13 NZP CSI-RS resource is obtained by aggregating threelegacy 4 port CSI-RS resources (to form a 12 port NZP CSI-RS resource)or two legacy 8 port CSI-RS resources (to form a 16 port NZP CSI-RSresource). It should be noted that all NZP CSI-RS resource aggregatedtogether are located in the same subframe. Examples of forming 12 portand 16 port NZP CSI-RS resources are shown in FIGS. 7A and 7B, in whichFIG. 7A illustrates an example of aggregating three 4-port resources toform a 12-port NZP CSI-RS Resource; and FIG. 7B illustrates an exampleof aggregating two 8-port resources to form a 16-port NZP CSI-RSResource, each 4-port resource and 8-port being aggregated together islabeled with the same number. In a given subframe, it is possible tohave three 12-port resource configurations (i.e., nine out of ten 4-portresources used) and two 16-port resource configurations (i.e., four outof five 8-port resources used). The following port numbering is used forthe aggregated NZP CSI-RS resources:

-   -   The aggregated port numbers are 15, 16, 17, 18, 19, 20, 21, 22,        23, 24, 25, 26, 27, 28, 29, 30 (for 16 NZP CSI-RS ports);    -   The aggregated port numbers are 15, 16, 17, 18, 19, 20, 21, 22,        23, 24, 25, 26 (for 12 NZP CSI-RS ports).

In addition, Rel-13 NZP CSI-RS design supports two different OCClengths. It is possible to multiplex antenna ports using OCC lengths twoand four for both 12-port and 16-port NZP CSI-RS.

NZP CSI-RS Designs with OCC Length 2

FIG. 8 shows the NZP CSI-RS design for the case of 12 ports with OCClength 2, where different 4-port resources are denoted by the alphabetsA-J. In FIG. 8 , the different 4-port NZP CSI-RS resources are denotedby the alphabets A-J. For instance, 4-port resources A, F, and J couldbe aggregated to form a 12-port NZP CSI-RS resource. The length 2 OCC isapplied across two REs with the same sub-carrier index and adjacent OFDMsymbol indices (for instance, OCC 2 is applied to the REs with OFDMsymbol indices 5-6 and sub-carrier index 9 in slot 0).

FIG. 9 shows the NZP CSI-RS design for the case of 16 ports with OCClength 2, where the different 8 port resources are shown in the legendof FIG. 9 , and the resources elements with the same alphabet form oneCDM group within each 8 port resource. In FIG. 9 , the different 8-portNZP CSI-RS resources are shown in the legend. For instance, 8-port NZPCSI-RS resources 1 and 3 could be aggregated to form a 16-port NZPCSI-RS resource. The length 2 OCC is applied across two REs with thesame sub-carrier index and adjacent OFDM symbol indices (for instance,OCC 2 is applied to the REs with OFDM symbol indices 2-3 and sub-carrierindex 7 in slot 1).

For the OCC length 2 case (i.e., when higher layer parameter ‘cdmType’is set to cdm2 or when ‘cdmType’ is not configured by Evolved UMTSTerrestrial Radio Access Network (EUTRAN)), the mapping of the referencesignal sequence r_(l,n) _(s) (m) of Equation 5 to the complex-valuedmodulation symbols a_(k,l) ^((p)) used as reference symbols on antennaport p is defined as:

$\begin{matrix}{a_{k,l}^{(p^{\prime})} = {w_{l^{''}} \cdot {r_{l,n_{s}}\left( m^{\prime} \right)}}} & {{Equation}6}\end{matrix}$ where $\begin{matrix}{k = {k^{\prime} + {12m} + \left\{ \begin{matrix}{{{{- 0}{for}\ p^{\prime}} \in \left\{ {15,16} \right\}},\ {{normal}{cyclic}\ {prefix}}} \\{{{{- 6}{for}\ p^{\prime}} \in \left\{ {17,18} \right\}},{{normal}{cyclic}\ {prefix}\ }} \\{{{{- 1}\ {for}\ p^{\prime}} \in \left\{ {{19},{20}} \right\}},\ {{normal}{cyclic}\ {prefix}}} \\{{{{- 7}\ {for}\ p^{\prime}} \in \left\{ {{21},{22}} \right\}},\ {{normal}{cyclic}\ {prefix}}} \\{{{{- 0}\ {for}\ p^{\prime}} \in \left\{ {{15},16} \right\}},\ {{extended}\ {cylic}{prefix}}} \\{{{{- 3}\ {for}\ p^{\prime}} \in \left\{ {{17},{18}} \right\}},\ {{extended}\ {cylic}{prefix}}} \\{{{{- 6}\ {for}\ p^{\prime}} \in \left\{ {{19},{20}} \right\}},\ {{extended}\ {cylic}{prefix}}} \\{{{{- 9}\ {for}\ p^{\prime}} \in \left\{ {{21},{22}} \right\}},\ {{extended}\ {cylic}{prefix}}}\end{matrix} \right.}} & {{Equation}7}\end{matrix}$ $l = {l^{\prime} + \left\{ \begin{matrix}l^{''} & {{{{CSI}{reference}{signal}{configurations}0} - 19},{{normal}{cyclic}{prefix}}} \\{2l^{''}} & {{{{CSI}{reference}{signal}{configurations}20} - 31},{{normal}{cyclic}{prefix}}} \\l^{''} & {{{{CSI}{reference}{signal}{configurations}0} - 27},{{normal}{cyclic}{prefix}}}\end{matrix} \right.}$ $w_{l^{''}} = \left\{ \begin{matrix}1 & {p^{\prime} \in \left\{ {15,17,19,21} \right\}} \\\left( {- 1} \right)^{l^{''}} & {p^{\prime} \in \left\{ {16,18,20,22} \right\}}\end{matrix} \right.$ l^(″) = 0, 1 m = 0, 1, …, N_(RB)^(DL) − 1$m^{\prime} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}$

In Equation 6-Equation 7, N_(RB) ^(DL) represents the downlinktransmission bandwidth; the indices k′ and l′ indicate the subcarrierindex (starting from the bottom of each RB) and the OFDM symbol index(starting from the right of each slot). The mapping of different (k′,l′) pairs to different CSI-RS resource configurations is given in Table2.

TABLE 2 Mapping from CSI reference signal configuration to ^((k′, l′))for normal cyclic prefix 1 or 2 4 8 Normal Special Normal Special NormalSpecial CSI-RS subframe subframe subframe subframe subframe subframeconfig. (k′, l′) n_(s)′ (k′, l′) n_(s)′ (k′, l′) n_(s)′ (k′, l′) n_(s)′(k′, l′) n_(s)′ (k′, l′) n_(s)′ 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 (9, 5) 0(9, 5) 0 (9, 5) 0 1 (11, 2) 1 (11, 5) 0 (11, 2) 1 (11, 5) 0 (11, 2) 1(11, 5) 0 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7,2) 1 (7, 5) 0 (7, 2) 1 (7, 5) 0 (7, 2) 1 (7, 5) 0 4 (9, 5) 1 (9, 5) 1(9, 5) 1 5 (8, 5) 0 (8, 5) 0 (8, 5) 0 (8, 5) 0 6 (10, 2) 1 (10, 5) 0(10, 2) 1 (10, 5) 0 7 (8, 2) 1 (8, 2) 1 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6,5) 0 (6, 2) 1 (6, 5) 0 9 (8, 5) 1 (8, 5) 1 10 (3, 5) 0 (3, 5) 0 11 (2,5) 0 (2, 5) 0 12 (5, 2) 1 (5, 5) 0 13 (4, 2) 1 (4, 5) 0 14 (3, 2) 1 (3,2) 1 15 (2, 2) 1 (2, 2) 1 16 (1, 2) 1 (1, 5) 0 17 (0, 2) 1 (0, 5) 0 18(3, 5) 1 19 (2, 5) 1 20 (11, 1) 1 (11, 1) 1 (11, 1) 1 21 (9, 1) 1 (9, 1)1 (9, 1) 1 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 23 (10, 1) 1 (10, 1) 1 24(8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1)1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

The quantity p′ for the case of OCC length 2 is related to the antennaport number p as follows:

-   -   p=p′ for CSI-RS using up to 8 antenna ports;    -   when higher-layer parameter ‘cdmType’ is set to cdm2 for CSI-RS        using more than 8 antenna ports, the following:

$\begin{matrix}{p = \left\{ \begin{matrix}{p^{\prime} + {\frac{N_{ports}^{CSI}}{2}i}} & {{{for}p^{\prime}} \in \left\{ {15,\ldots,{15 + {N_{ports}^{CSI}/2} - 1}} \right\}} \\\begin{matrix}{p^{\prime} + \frac{N_{ports}^{CSI}}{2}} \\\left( {i + N_{res}^{CSI} - 1} \right)\end{matrix} & \begin{matrix}{{{for}p^{\prime}} \in \left\{ {{15 + {N_{ports}^{CSI}/2}},\ldots,{15 +}} \right.} \\\left. {N_{ports}^{CSI} - 1} \right\}\end{matrix}\end{matrix} \right.} & {{Equation}8}\end{matrix}$

wherein i∈{0, 1, . . . , N_(res) ^(CSI)−1} is the CSI resource number;N_(res) ^(CSI) and N_(ports) ^(CSI) respectively denote the number ofaggregated CSI-RS resources and the number of antenna ports peraggregated CSI-RS resource. As stated above, the allowed values ofN_(res) ^(CSI) and N_(ports) ^(CSI) for the cases of 12 and 16 port NZPCSI-RS design are given in Table 3.

Total number of Number of antenna Number of CSI-RS antenna ports portsper resources resources N_(res) ^(CSI)N_(ports) ^(CSI) N_(ports) ^(CSI)N_(res) ^(CSI) 12 4 3 16 8 2

NZP CSI-RS Designs with OCC Length 4

FIG. 10 shows the NZP CSI-RS design for the case of 12 ports with OCClength 4, where 4-port resources are denoted by the alphabets A-J. InFIG. 10 , the different 4-port NZP CSI-RS resources are denoted by thealphabets A-J. For instance, 4-port resources A, F, and J could beaggregated to form a 12-port NZP CSI-RS resource. A length 4 OCC isapplied within a CDM group where a CDM group consists of the 4 resourceelements used for mapping legacy 4-port CSI-RS. That is, the resourceelements labeled with the same alphabet in FIG. 10 comprise one CDMgroup. A length-4 OCC is given in Equation 9.

$\begin{matrix}{W_{4} = \begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}} & {{Equation}9}\end{matrix}$

FIG. 11 shows the NZP CSI-RS design for the case of 16 ports with OCClength 4, where different 8-port resources are shown in the legend, theresource elements with the same alphabet form one CDM group within an8-port CSI-RS resource. In FIG. 11 , the different 8-port NZP CSI-RSresources are shown in the legend. For instance, 8-port NZP CSI-RSresources 1 and 3 could be aggregated to form a 16-port NZP CSI-RSresource. Each 8-port resource is further partitioned into two groups of4 adjacent REs and each of these groups comprises a CDM group. In FIG.11 , the REs with labels A and B form one legacy 8-port resource where Aand B are the CDM groups within this resource. An OCC with length 4 isapplied within each CDM group. In the rest of the document, the CDMgroups corresponding to REs with labels A and B within each 8-port NZPCSI-RS resource configuration are referred to as CDM groups i and ii,respectively.

For the OCC length 4 case (i.e., when higher layer parameter ‘cdmType’is set to cdm4), the mapping of the reference signal sequence r_(l,n)_(s) (m) of Equation 5 to the complex-valued modulation symbols a_(k,l)^((p)) used as reference symbols on antenna port p are defined as:

$\begin{matrix}{a_{k,l}^{(p^{\prime})} = {{w_{p^{\prime}}(i)} \cdot {r_{l,n_{s}}\left( m^{\prime} \right)}}} & {{Equation}10}\end{matrix}$ where $\begin{matrix}{k = {k^{\prime} + {12m} - \left\{ \begin{matrix}k^{''} & \begin{matrix}{{{{for}\ p^{\prime}} \in \left\{ {15,16,19,20} \right\}},\ } \\{{{normal}{cyclic}\ {prefix}},{N_{ports}^{CSI} = 8}}\end{matrix} \\{k^{''} + 6} & \begin{matrix}{{{{for}\ p^{\prime}} \in \left\{ {17,18,21,22} \right\}},\ } \\{{{normal}{cyclic}\ {prefix}},{N_{ports}^{CSI} = 8}}\end{matrix} \\{6k^{''}} & \begin{matrix}{{{{for}\ p^{\prime}} \in \left\{ {15,16,17,18} \right\}},\ } \\{{{normal}{cyclic}\ {prefix}},{N_{ports}^{CSI} = 4}}\end{matrix}\end{matrix} \right.}} & {{Equation}11}\end{matrix}$ $l = {l^{\prime} + \left\{ \begin{matrix}l^{''} & \begin{matrix}{{{{CSI}{reference}{signal}{configurations}0} - 19},} \\{{normal}{cyclic}{prefix}}\end{matrix} \\{2l^{''}} & \begin{matrix}{{{{CSI}{reference}{signal}{configurations}20} - 31},} \\{{normal}{cyclic}{prefix}}\end{matrix}\end{matrix} \right.}$ l^(″) = 0, 1 k^(′′) = 0, 1 i = 2k^(′′) + l^(′′)m = 0, 1, …, N_(RB)^(DL) − 1$m^{\prime} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}$

In Equation 10-Equation 11, N_(RB) ^(DL) represents the downlinktransmission bandwidth; N_(ports) ^(CSI) denotes the number of antennaports per aggregated CSI-RS resource; the indices k′ and l′ indicate thesubcarrier index (starting from the bottom of each RB) and the OFDMsymbol index (starting from the right of each slot). The mapping ofdifferent (k′, l′) pairs to different CSI-RS resource configurations isgiven in Table 2. Furthermore, w_(p′)(i) in Equation 10 is given byTable 4, where Table 4 illustrates the sequence w_(p′)(i) for CDM4.

p′ N_(ports) ^(CSI) = 4 N_(ports) ^(CSI) = 8 [w_(p′)(0) w_(p′)(1)w_(p′)(2) w_(p′)(3)] 15 15, 17 [1 1 1 1] 16 16, 18 [1 −1 1 −1] 17 19, 21[1 1 −1 −1] 18 20, 22 [1 −1 −1 1]

When higher-layer parameter ‘cdmType’ is set to cdm4 for CSI-RS usingmore than 8 antenna ports, antenna port numberp=iN _(ports) ^(CSI) +p′  Equation 12

where p′∈{15, 16, . . . , 15+N_(ports) ^(CSI)−1} for CSI-RS resourcenumber i∈{0, 1, . . . , N_(res) ^(CSI)−1}.

SUMMARY

Some embodiments advantageously provide a method and system for codedivision multiplexing, CDM, aggregation configurations for reducingperformance losses due to channel variations in wireless communications.

Disadvantages of one approach in CDM-8 design include that (1) it willsuffer performance losses if the channel varies significantly over 9OFDM symbols due to loss of orthogonality in the CDM-8 group, and (2) ithas higher CSI-RS overhead than required. Other disadvantages of otherCDM-8 approaches include (1) the scheme does not prevent performancelosses if the channel varies significantly over 9 OFDM symbols due toloss of orthogonality in the CDM-8 group, and (2) the scheme is notsuitable for 24 ports. For 24-ports, if CDM-4 aggregation is donearbitrarily (as discussed above) to form a CDM-8 group, this can stillresult in performance losses if the channel varies significantly over 9OFDM symbols due to loss of orthogonality in the CDM-8 group asillustrated in the example of FIG. 15 .

Certain aspects and their embodiments of the present disclosure mayprovide solutions to these or other problems. In a first solution, thelength 8 orthogonal cover code is achieved by aggregating two length 4orthogonal cover code groups belonging to a pair of legacy LTE CSI-RSresources where the pair of legacy resources are chosen from aconstrained set of pairs that are chosen to minimize loss oforthogonality of the length 8 cover code due to channel variations intime domain. In this solution, the network node signals to the wirelessdevice pairs of legacy CSI-RS resources that are selected during theaggregation of length 4 orthogonal cover code groups or indices thatrepresent pairs of legacy CSI-RS resources that are selected during theaggregation of length 4 orthogonal cover code groups.

In a second solution, the length 8 orthogonal cover code is achieved byaggregating two length 4 orthogonal cover code groups belonging to apair of legacy LTE CSI-RS resources where the pair of legacy resourcesand which length 4 orthogonal cover code groups are selected from aconstrained set of pairs that are chosen to minimize loss oforthogonality of the length 8 cover code due to channel variations intime and frequency domains. In this solution, where the network nodesignals to the wireless device one or more 8-port CSI-RS configurationand CDM-4 group combination pairs that are chosen during the aggregationof length 4 orthogonal cover code groups or one or more indices thatrepresent 8-port CSI-RS configuration and CDM-4 group combination pairsthat are chosen during the aggregation of length 4 orthogonal cover codegroups.

In one embodiment of the disclosure, a method of increasing the energyin a reference signal while limiting its bandwidth, the methodcomprising at least one of:

-   -   a) Selecting a first and a second reference signal        configuration, where at least one of the following are met:        -   i) the first and the second reference signal configurations            are selected from a predefined set of reference signal            configurations        -   ii) each reference signal configuration identifies a set of            frequency and time locations of resource elements        -   iii) each resource element is associated with an element of            a reference sequence        -   iv) a maximum time separation of the time locations in the            first and second reference signal configurations is a first            maximum separation        -   v) the largest maximum time separation of the time locations            over all possible pairs of reference signal configurations            in the predefined set is a largest maximum separation, and        -   vi) the largest maximum time separation is greater than the            first maximum separation;    -   b) forming a reference signal by applying a first cover sequence        to a first and a second set of reference signal sequences, where        at least one of the following are met:        -   i) the first reference signal sequence corresponds to a            first subset of reference elements of the first reference            signal configuration        -   ii) the second reference signal sequence corresponds to a            second subset of reference elements of the second reference            signal configuration        -   iii) the first cover sequence is associated with an antenna            port,        -   iv) the first cover sequence is selected from a set of cover            sequences,        -   v) and each cover sequence is orthogonal to every other            cover sequence in the set; and    -   c) transmitting the reference signal in the first and second        subsets of reference elements.

According to one aspect of this embodiment, at least one of thefollowing are met: a maximum frequency separation of the frequencylocations in the first and second subsets is a second maximumseparation, the largest maximum frequency separation of the frequencylocations over all possible pairs of reference elements in the first andsecond reference signal configurations is a largest maximum separationand the largest maximum frequency separation is greater than the secondmaximum separation.

According to one aspect of this embodiment,

-   -   d) Transmitting N distinct reference signals in the first and        second subsets of resource elements, wherein at least one of the        following are met:        -   i) each reference signal is associated with an antenna port            number, thereby creating a set of antenna port numbers for            the N distinct reference signals        -   ii) the antenna port numbers are consecutive, such that any            antenna port number in the set n₁ is related to another            antenna port n₂ in the set according to: n₁=n₂+1 or n₁=n₂−1.

According to another embodiment of the disclosure, a method oftransmitting CSI-RS ports in multiple aggregated legacy LTE CSI-RSresources using a length 8 orthogonal cover code. According to one ormore embodiments of the disclosure, the length 8 orthogonal cover codeis achieved by aggregating two length 4 orthogonal cover code groupsbelonging to a pair of legacy LTE CSI-RS resources where the pair oflegacy resources are chosen from a constrained set of pairs that arechosen to minimize loss of orthogonality of the length 8 cover code dueto channel variations in time domain. According to one aspect of thisembodiment, a network node signals to a wireless device the pairs oflegacy CSI-RS resources that are chosen during the aggregation of length4 orthogonal cover code groups or one or more indices that represent thepairs of legacy CSI-RS resources that are chosen during the aggregationof length 4 orthogonal cover code groups.

According to one or more embodiments of the disclosure, the length 8orthogonal cover code is achieved by aggregating two length 4 orthogonalcover code groups belonging to a pair of legacy LTE CSI-RS resourceswhere the pair of legacy resources and which length 4 orthogonal covercode groups are chosen from a constrained set of pairs that are chosento minimize loss of orthogonality of the length 8 cover code due tochannel variations in time and frequency domains. According to oneaspect of this embodiment, the network node signals to the wirelessdevice one or more 8-port CSI-RS configuration and CDM-4 groupcombination pairs that are chosen during the aggregation of length 4orthogonal cover code groups or one or more indices that represent oneor more 8-port CSI-RS configuration and CDM-4 group combination pairsthat are chosen during the aggregation of length 4 orthogonal cover codegroups.

According to one or more embodiments of the disclosure, the aggregationof length 4 orthogonal cover codes with the same group number in a pairof 8-port CSI-RS configurations is allowed. According to one or moreembodiments of the disclosure, the aggregation of length 4 orthogonalcover code groups within the same 8-port CSI-RS configuration is allowedin combination with the aggregation of length 4 orthogonal cover codesbetween a pair of 8-port CSI-RS configurations.

According to one embodiment of the disclosure, a network node isprovided. The network node includes processing circuitry configured to:select a first set and second set of reference signal resources in asubframe, and aggregate the first set and second set of reference signalresources to the subframe to form a code division multiplexing, CDM,aggregation configuration. The first set and second set of referencesignal resources in the subframe satisfies a temporal criterion suchthat any two resource elements in the first set and second set ofreference signal resources have up to a maximum time separation of sixOFDM symbols. The first set and second set of reference signal resourcesin the subframe satisfies a frequency criterion such that any tworesource elements in the first set and second set of reference signalresources have up to a maximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration. According to oneembodiment of this aspect, the first set of reference signal resourcesin the subframe includes a subset of resources from an eight port CSI-RSresource configuration. The second set of reference signal resources inthe subframe includes a subset of resources in a different eight portCSI-RS resource configuration different from the eight port CSI-RSresource configuration corresponding to the first set of referencesignal resources. The CDM aggregation configuration has an orthogonalcover code of length eight. According to one embodiment of this aspect,processing circuitry is further configured to communicate the CDMaggregation configuration to a wireless device.

According to another aspect of the disclosure, a method is provided. Afirst set and second set of reference signal resources. The first setand second set of reference signal resources are aggregated to thesubframe to form a code division multiplexing, CDM, aggregationconfiguration. The first set and second set of reference signalresources in the subframe satisfy a temporal criterion such that any tworesource elements in the first set and second set of reference signalresources have up to a maximum time separation of six OFDM symbols. Thefirst set and second set of reference signal resources in the subframesatisfy a frequency criterion such that any two resource elements in thefirst set and second set of reference signal resources have up to amaximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration. According to oneembodiment of this aspect, the first set of reference signal resourcesin the subframe includes a subset of resources from an eight port CSI-RSresource configuration. The second set of reference signal resources inthe subframe includes a subset of resources in a different eight portCSI-RS resource configuration different from the eight port CSI-RSresource configuration corresponding to the first set of referencesignal resources. The CDM aggregation configuration has an orthogonalcover code of length eight.

According to another aspect of the disclosure, a wireless device isprovided. The wireless device includes processing circuitry configuredto receive a CDM aggregation configuration corresponding to anaggregated first set and second set of reference signal resources in asubframe. The processing circuitry is further configured to performchannel estimation based on the CDM aggregation configuration. The firstset and second set of reference signal resources in the subframe satisfya temporal criterion such that any two resource elements in the firstset and second set of reference signal resources have up to a maximumtime separation of six OFDM symbols. The first set and second set ofreference signal resources in the subframe satisfy a frequency criterionsuch that any two resource elements in the first set and second set ofreference signal resources have up to a maximum frequency separation ofsix subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration. According to oneembodiment of this aspect, the first set of reference signal resourcesin the subframe includes a subset of resources from an eight port CSI-RSresource configuration. The second set of reference signal resources inthe subframe includes a subset of resources in a different eight portCSI-RS resource configuration different from the eight port CSI-RSresource configuration corresponding to the first set of referencesignal resources. The CDM aggregation configuration has an orthogonalcover code of length eight. According to one embodiment of this aspect,the processing circuitry is further configured to map the selected firstset and second set of reference signal resources in the subframe to aplurality of antenna ports.

According to another aspect of the disclosure, a method for a wirelessdevice is provided. A CDM aggregation configuration corresponding to anaggregated first set and second set of reference signal resources in asubframe is received. Channel estimation is performed based on the CDMaggregation configuration. The first set and second set of referencesignal resources in the subframe satisfy a temporal criterion such thatany two resource elements in the first set and second set of referencesignal resources have up to a maximum time separation of six OFDMsymbols. The first set and second set of reference signal resources inthe subframe satisfy a frequency criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration. According to oneembodiment of this aspect, the first set of reference signal resourcesin the subframe includes a subset of resources from an eight port CSI-RSresource configuration. The second set of reference signal resources inthe subframe includes a subset of resources in a different eight portCSI-RS resource configuration different from the eight port CSI-RSresource configuration corresponding to the first set of referencesignal resources. The CDM aggregation configuration has an orthogonalcover code of length eight. According to one embodiment of this aspect,the selected first set and second set of reference signal resources inthe subframe are mapped to a plurality of antenna ports.

According to another aspect of the disclosure, a network node isprovided. The network node includes an aggregation processing moduleconfigured to select a first set and second set of reference signalresources in a subframe, aggregate the first set and second set ofreference signal resources to the subframe to form a code divisionmultiplexing, CDM, aggregation configuration. The first set and secondset of reference signal resources in the subframe satisfy a temporalcriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum timeseparation of six OFDM symbols. The first set and second set ofreference signal resources in the subframe satisfy a frequency criterionsuch that any two resource elements in the first set and second set ofreference signal resources have up to a maximum frequency separation ofsix subcarriers.

According to another aspect of the disclosure, a wireless device isprovided. The wireless device includes a channel processing moduleconfigured to receive a CDM aggregation configuration corresponding toan aggregated first set and second set of reference signal resources ina subframe. The channel processing module is further configured toperform channel estimation based on the CDM aggregation configuration.The first set and second set of reference signal resources in thesubframe satisfies a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources in the subframe satisfies afrequency criterion such that any two resource elements in the first setand second set of reference signal resources have up to a maximumfrequency separation of six subcarriers.

According to one aspect of the disclosure, a network node is provided.The network node includes processing circuitry configured to: select afirst set and second set of reference signal resources in a subframe andaggregate the first set and second set of reference signal resources inthe subframe to form a code division multiplexing, CDM, aggregationconfiguration. The first set and second set of reference signalresources in the subframe satisfy a temporal criterion such that any tworesource elements in the first set and second set of reference signalresources have up to a maximum time separation of six OFDM symbols. Thefirst set and second set of reference signal resources in the subframesatisfy a frequency criterion such that any two resource elements in thefirst set and second set of reference signal resources have up to amaximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration.

According to one embodiment of this aspect, the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration. The second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources. The CDM aggregation configuration has anorthogonal cover code of length eight. According to one embodiment ofthis aspect, the processing circuitry is further configured tocommunicate the CDM aggregation configuration to a wireless device.According to one embodiment of this aspect, the CDM aggregationconfiguration is an aggregation of two CDM-4 groups.

According to another aspect of the disclosure, a method is provided. Afirst set and second set of reference signal resources in a subframe areselected. The first set and second set of reference signal resources areaggregated to the subframe to form a code division multiplexing, CDM,aggregation configuration. The first set and second set of referencesignal resources in the subframe satisfy a temporal criterion such thatany two resource elements in the first set and second set of referencesignal resources have up to a maximum time separation of six OFDMsymbols. The first set and second set of reference signal resources inthe subframe satisfy a frequency criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration. According to oneembodiment of this aspect, the first set of reference signal resourcesin the subframe includes a subset of resources from an eight port CSI-RSresource configuration. The second set of reference signal resources inthe subframe includes a subset of resources in a different eight portCSI-RS resource configuration different from the eight port CSI-RSresource configuration corresponding to the first set of referencesignal resources. The CDM aggregation configuration having an orthogonalcover code of length eight.

According to one embodiment of this aspect, the CDM aggregationconfiguration is communicated to a wireless device. According to oneembodiment of this aspect, the CDM aggregation configuration is anaggregation of two CDM-4 groups.

According to another aspect of the disclosure, a wireless device isprovided. The wireless device includes processing circuitry configuredto receive a CDM aggregation configuration corresponding to anaggregated first set and second set of reference signal resources in asubframe and perform channel estimation based on the CDM aggregationconfiguration. The first set and second set of reference signalresources satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources satisfy a frequencycriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum frequencyseparation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration.

According to one embodiment of this aspect, the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration. The second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources. The CDM aggregation configuration havingan orthogonal cover code of length eight. According to one embodiment ofthis aspect, the processing circuitry is further configured to map theselected first set and second set of reference signal resources in thesubframe to a plurality of antenna ports. According to one embodiment ofthis aspect, the CDM aggregation configuration is an aggregation of twoCDM-4 groups.

According to another aspect of the disclosure, a method for a wirelessdevice is provided. A CDM aggregation configuration corresponding to anaggregated first set and second set of reference signal resources in asubframe is received. The first set and second set of reference signalresources. Channel estimation is performed based on the CDM aggregationconfiguration. The first set and second set of reference signalresources satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources satisfy a frequencycriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum frequencyseparation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration.

According to one embodiment of this aspect, the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration. The second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources. The CDM aggregation configuration has anorthogonal cover code of length eight.

According to one embodiment of this aspect, the CDM aggregationconfiguration is an aggregation of two CDM-4 groups. According to oneembodiment of this aspect, the selected first set and second set ofreference signal resources in the subframe are mapped to a plurality ofantenna ports.

According to another aspect of the disclosure, a network node isprovided. The network node includes an aggregation processing moduleconfigured to: select a first set and second set of reference signalresources in a subframe and aggregate the first set and second set ofreference signal resources to the subframe to form a code divisionmultiplexing, CDM, aggregation configuration. The first set and secondset of reference signal resources in the subframe satisfy a temporalcriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum timeseparation of six OFDM symbols. The first set and second set ofreference signal resources in the subframe satisfy a frequency criterionsuch that any two resource elements in the first set and second set ofreference signal resources have up to a maximum frequency separation ofsix subcarriers.

According to one aspect of the disclosure, a wireless device isprovided. The wireless device includes a channel processing moduleconfigured to: receive a CDM aggregation configuration corresponding toan aggregated first set and second set of reference signal resources ina subframe, and perform channel estimation based on the CDM aggregationconfiguration. The first set and second set of reference signalresources satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources satisfy a frequencycriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum frequencyseparation of six subcarriers.

According to one embodiment of this aspect, the channel processingmodule is further configured to communicate the CDM aggregationconfiguration to a wireless device. According to one embodiment of thisaspect, the CDM aggregation configuration is communicated to a wirelessdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 illustrates a basic LTE downlink physical resource;

FIG. 2 illustrates an LTE time-domain structure;

FIG. 3 illustrates a physical resource block within a downlink subframe;

FIG. 4 illustrates a transmission structure of precoded spatialmultiplexing mode in LTE;

FIG. 5 illustrates a two-dimensional antenna array elements;

FIG. 6 illustrates a resource element grid;

FIG. 7A illustrates an example of aggregating three 4-port resources toform a 12-port NZP CSI-RS Resource, and FIG. 7B illustrates an exampleof aggregating two 8-port resources to form a 16-port NZP CSI-RSResource, each 4-port resource and 8-port being aggregated together islabeled with the same number;

FIG. 8 illustrates NZP CSI-RS design for the case of 12 ports with OCClength 2, where different 4-port resources are denoted by the alphabetsA-J;

FIG. 9 illustrates NZP CSI-RS design for the case of 16 ports with OCClength 2, where the different 8 port resources;

FIG. 10 illustrates NZP CSI-RS design for the case of 12 ports with OCClength 4, where 4-port resources are denoted by the alphabets A-J;

FIG. 11 illustrates NZP CSI-RS design for the case of 16 ports with OCClength 4, where different 8-port resources are shown in the legend, theresource elements with the same alphabet form one CDM group within an8-port CSI-RS resource;

FIG. 12 illustrates a CDM-8 pattern design;

FIG. 13 illustrates a 32-port example;

FIG. 14 illustrates CDM-8 group patterns;

FIG. 15 illustrates a 24-port, CDM-4 aggregation performed in anarbitrary way;

FIG. 16 is a block diagram of a system for code division multiplexing,CDM, aggregation configurations for wireless communications inaccordance with the principles of some embodiments of the presentdisclosure;

FIG. 17 is a flow diagram of one exemplary embodiment of the aggregationprocess of aggregation code in accordance with the principles of someembodiments of the disclosure;

FIG. 18 is a diagram of CDM-8 groups formed by aggregating CDM-4 groupsin accordance with the principles of some embodiments of the disclosure;

FIG. 19 is a diagram of aggregating CDM-4 groups that could result inperformance losses;

FIG. 20 is a diagram of CDM-4 aggregation within 8-port CSI-RS resourcecombined with CDM-4 aggregation across a pair of 8-port CSI-RS resourcesin accordance with the principles of some embodiments of the disclosure;

FIG. 21 is a flow diagram of one exemplary embodiment of the channelprocess of channel code 24 in accordance with the principles of thedisclosure; and

FIG. 22 is an example of antenna port numbering with CDM8 and 32 portswith {k_0,k_1,k_2,k_3}={0,4,1,3}.

DETAILED DESCRIPTION

Number of NZP CSI-RS Configurations

The number of different 12 port and 16 port CSI-RS configurations in asubframe in the LTE Release 13 NZP CSI-RS designs are three and two,respectively. That is, for the 12 port case, three different CSI-RSconfigurations can be formed where each configuration is formed byaggregating three legacy 4-port CSI-RS configurations. This will consume36 CSI-RS REs of the 40 CSI-RS REs available for CSI-RS within aphysical resource block (PRB). For the 16 port case, two differentCSI-RS configurations can be formed where each configuration is formedby aggregating two legacy 8-port CSI-RS configurations. This willconsume 32 CSI-RS REs of the 40 CSI-RS REs available for CSI-RS within aresource block (RB).

NZP CSI-RS for 24 and 32 Ports and CDM-8 in LTE Release 14

In LTE Release 14, a NZP CSI-RS configuration with 24 and 32 ports isachieved by aggregating three and four legacy 8-port CSI-RS resources.For instance, in the case of 24 ports three out of the five legacy8-port resources shown in FIG. 9 and FIG. 11 are aggregated together.Both CDM-2 (i.e., OCC length-2 code) and CDM-4 (i.e., OCC length-4 code)are supported for 24 and 32 ports in Release 14.

In addition, CDM-8 will also be supported in LTE Release 14 for NZPCSI-RS with 24 and 32 ports. A CDM-8 can be defined using a length-8 OCCgiven by Equation 13. The main motivation for introducing CDM-8 inRelease-14 is to support full power utilization for NZP CSI-RStransmission.

$\begin{matrix}{W_{8} = \begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 \\1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 \\1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 \\1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1}\end{bmatrix}} & {{Equation}13}\end{matrix}$

A CDM-8 pattern design is proposed in R1-166341, “CSI-RS design for{20,24,28,32} ports”, China Academy of Telecommunications Technology(CATT), 3GPP TSG RAN WG1 Meeting #86, Aug. 22-26, 2016, Gothenburg,Sweden, which is reproduced in FIG. 12 . The REs with the same letter inFIG. 12 represent a Code Division Multiplexing (CDM)-8 group. The majordrawbacks of this design are as follows:

Each CDM-8 group is spread across 9 OFDM symbols (i.e., from symbol 5 inthe first slot to symbol 6 in the second slot). In this design, theorthogonality of the length-8 OCC depends on the flatness of the channelin the time domain. That is, the channel should not vary significantlyover the 9 OFDM symbols over which each CDM-8 group is spread. However,in practice, the channel can vary over 9 OFDM symbols due to wirelessdevice mobility and phase drift. Hence, when the channel varies over 9OFDM symbols due to wireless device mobility or phase drift, theorthogonality of these CDM-8 groups may be destroyed.

-   -   The CDM-8 design has extra CSI-RS overhead. For instance, for a        32 port NZP CSI-RS design, this design will use all the CSI-RS        REs labeled A-D. Noting that these CSI-RS REs are distributed        over all 5 legacy 8-port CSI-RS resources (i.e., resources 0-1        indicated in FIG. 12 ), then these 5 legacy 8-port CSI-RS        resources cannot be used for other wireless devices and legacy        wireless devices always have to perform Physical Downlink Shared        Channel (PDSCH) rate matching around all 40 CSI-RS REs in these        resources. This will result in higher CSI-RS overhead than        needed (i.e. a CSI-RS RE overhead increase of

${1 - \frac{40}{32}} = {25\%}$in a subframe carrying CSI-RS transmission). The problem is even worsefor 24 port NZP CSI-RS design since all 40 CSI-RS REs cannot be used forother wireless devices (i.e., a CSI-RS RE overhead increase of

${1 - \frac{40}{24}} = {67\%}$in a subframe carrying CSI-RS transmission).

A CDM-8 approach is proposed in the following references: R1-166519,“Performance comparison of CDM-4 and CDM-8 for CSI-RS”, IntelCorporation, 3GPP TSG RAN WG1 Meeting #86, Aug. 22-26, 2016, Gothenburg,Sweden and R1-167996, “WF on CDM aggregation for NP CSI-RS”, Samsung,Xinwei, Ericsson, 3GPP TSG RAN WG1 Meeting #86, Aug. 22-26, 2016,Gothenburg, Sweden, where the CDM-8 group is attained by aggregating twoCDM-4 groups in two different legacy 8-port CSI-RS resources. A 32-portexample is shown in FIG. 13 , where the CDM-8 group denoted by A isformed by aggregating a CDM-4 group from legacy 8-port CSI-RS resource 0and a CDM-4 group from legacy 8-port CSI-RS resource 2. It is furtherproposed that the aggregation of the CDM-4 groups is done in the orderof the CSI-RS configuration index. For instance, if the four legacy8-port CSI-RS resources being aggregated together are signaled by thenetwork node to the wireless device as {0, 1, 2, 4}, then legacy 8-portCSI-RS resources 0, 1, 2, and 4 correspond to CSI-RS resource numbersi=0, i=1, i=2, and i=3, respectively (note the CSI-RS resource number iis defined as in Equation 12). Then according to the aggregationcriterion in R1-167996, “WF on CDM aggregation for NP CSI-RS”, Samsung,Xinwei, Ericsson, 3GPP TSG RAN WG1 Meeting #86, August 22-26, 2016,Gothenburg, Sweden, CDM-4 groups in legacy 8-port CSI-RS resources 0 and1 (which correspond to i=0 and i=¹) are aggregated together to form aCDM-8 group. Similarly, CDM-4 groups in legacy 8-port CSI-RS resources 2and 4 (which correspond to i=2 and i=3) are aggregated together to forma CDM-8 group. This results in the CDM-8 group patterns shown in FIG. 13.

However, according to the CDM-8 aggregation criterion in R1-167996, “WFon CDM aggregation for NP CSI-RS”, Samsung, Xinwei, Ericsson, 3GPP TSGRAN WG1 Meeting #86, Aug. 22-26, 2016, Gothenburg, Sweden, if the fourlegacy 8-port CSI-RS resources being aggregated together are signaled bythe network node to the wireless device as {0, 4, 1, 2}, then legacy8-port CSI-RS resources 0, 4, 1, and 2 correspond to CSI-RS resourcenumbers i=0, i=1, i=2, and i=3, respectively (note the CSI-RS resourcenumber i is defined as in Equation 12). Then according to thisaggregation criterion, CDM-4 groups in legacy 8-port CSI-RS resources 0and 4 (which correspond to i=0 and i=1) are aggregated together to forma CDM-8 group. Similarly, CDM-4 groups in legacy 8-port CSI-RS resources1 and 2 (which correspond to i=² and i=³) are aggregated together toform a CDM-8 group. This results in the CDM-8 group patterns shown inFIG. 14 . A disadvantage with this CDM-8 grouping is that CDM-8 groupsdenoted by A and D in FIG. 14 are spread across 9 OFDM symbols. Hence,when the channel varies over 9 OFDM symbols due to wireless devicemobility or phase drift, the orthogonality of these CDM-8 groups may bedestroyed.

A second disadvantage of the approaches described above is how tosupport the CDM-8 aggregation for 24 ports. Since there are an oddnumber (i.e., 3) of legacy 8-port CSI-RS resources being aggregatedtogether to form a 24-port NZP CSI-RS configuration, the approach ofaggregating CDM-4 groups in legacy 8-port CSI-RS resources withconsecutive CSI-RS resource numbers does not apply. This is due to thelack of a fourth legacy 8-port CSI-RS resource which would otherwise beused for CDM-4 aggregation with the third legacy 8-port CSI-RS resource.

It is possible to perform CDM-4 aggregation in an arbitrary fashion inthe case of 24-ports as shown in FIG. 15 . However, the resulting CDM-8group C in FIG. 15 is spread across 9 OFDM symbols. Hence, when thechannel varies over 9 OFDM symbols due to wireless device mobility orphase drift, the orthogonality of this CDM-8 group may be destroyed.

Some embodiments of the disclosure aim to solve at least some of theproblems with existing systems at least in part by providing for CDM-8designs via CDM-4 aggregation while minimizing the performance lossesdue to channel variations in the time and frequency directions. Someembodiments of the disclosure may provide for CDM-8 designs that doesnot involve any increase in CSI-RS overhead (i.e., 32 CSI-RS REs per PRBwill be used for 32 port NZP CSI-RS).

Note that although terminology from 3GPP LTE has been used in thisdisclosure, this should not be seen as limiting the scope of thedisclosure to only the aforementioned system. Other wireless systems,including New Radio (NR), Wide Band Code Division Multiple Access(WCDMA), WiMax, Ultra-Mobile Broadband (UMB) and Global Systems forMobile communications (GSM), may also benefit from exploiting the ideascovered within this disclosure. Also note that terminology such asnetwork node and wireless device should be considering non-limiting anddoes in particular not imply a certain hierarchical relation between thetwo; in general “eNodeB” could be considered as device 1 and “wirelessdevice” device 2, and these two devices communicate with each other oversome radio channel. Herein, we also focus on wireless transmissions inthe downlink, but some embodiments of the disclosure are equallyapplicable in the uplink.

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to CDM aggregation configurations for wirelesscommunications. Accordingly, components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments soas not to obscure the disclosure with details that will be readilyapparent to those of ordinary skill in the art having the benefit of thedescription herein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements.

The term wireless device used herein may refer to any type of wirelessdevice communicating with a network node and/or with another wirelessdevice in a cellular or mobile communication system. Examples of awireless device are user equipment (UE), target device, device to device(D2D) wireless device, machine type wireless device or wireless devicecapable of machine to machine (M2M) communication, PDA, iPAD, Tablet,mobile terminals, smart phone, laptop embedded equipped (LEE), laptopmounted equipment (LME), USB dongles etc.

The term “network node” used herein may refer to a radio network node oranother network node, e.g., a core network node, Mobile Switching Center(MSC), Mobility Management Entity (MME), Operations and Maintenance(O&M), Operations System Support (OSS), SON, positioning node (e.g.(Evolved Serving Mobile Location Center (E-SMLC)), Minimization DriveTest (MDT) node, etc.

The term “network node” or “radio network node” used herein can be anykind of network node comprised in a radio network which may furthercomprise any of base station (BS), radio base station, base transceiverstation (BTS), base station controller (BSC), radio network controller(RNC), evolved Node B (eNB or eNodeB), Node B, multi-standard radio(MSR) radio node such as MSR BS, relay node, donor node controllingrelay, radio access point (AP), transmission points, transmission nodes,Remote Radio Unit (RRU) Remote Radio Head (RRH), nodes in distributedantenna system (DAS) etc.

Note further, that functions described herein as being performed by awireless device or a network node may be distributed over a plurality ofwireless devices and/or network nodes. In other words, it iscontemplated that the functions of the network node and wireless devicedescribed herein are not limited to performance by a single physicaldevice and, in fact, can be distributed among several physical devices.

Referring now to drawing figures in which like reference designatorsrefer to like elements there is shown in FIG. 16 an exemplary system forcode division multiplexing, CDM, aggregation configurations for wirelesscommunications in accordance with the principles of some embodiments ofthe present disclosure and designated generally as “10.” System 10includes one or more wireless devices 12 a-12 n (collectively referredto as wireless device 12) and one or more network nodes 14 a-14 n(collectively referred to as network node 14), in communication witheach other via one or more communication networks using one or morecommunication protocols, where wireless device 12 and/or network node 14are configured to perform the processes described herein.

Wireless device 12 includes one or more communication interfaces 16 forcommunicating with one or more other wireless devices 12, network nodes14, and/or other elements in system 10. In one or more embodiments,communication interface 16 includes one or more transmitters and/or oneor more receivers. Wireless device 12 includes processing circuitry 18.Processing circuitry 18 includes processor 20 and memory 22. In additionto a traditional processor and memory, processing circuitry 18 maycomprise integrated circuitry for processing and/or control, e.g., oneor more processors and/or processor cores and/or FPGAs (FieldProgrammable Gate Array) and/or ASICs (Application Specific IntegratedCircuitry). Processor 20 may be configured to access (e.g., write toand/or reading from) memory 22, which may comprise any kind of volatileand/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM(Random Access Memory) and/or ROM (Read-Only Memory) and/or opticalmemory and/or EPROM (Erasable Programmable Read-Only Memory). Suchmemory 22 may be configured to store code executable by processor 20and/or other data, e.g., data pertaining to communication, e.g.,configuration and/or address data of nodes, etc.

Processing circuitry 18 may be configured to control any of the methodsand/or processes described herein and/or to cause such methods and/orprocesses to be performed, e.g., by wireless device 12. Processor 20corresponds to one or more processors 20 for performing wireless device12 functions described herein. Wireless device 12 includes memory 22that is configured to store data, programmatic software code and/orother information described herein. In one or more embodiments, memory22 is configured to store Channel code 24. For example, channel code 24includes instructions that, when executed by processor 20, causesprocessor 20 to perform the process discussed in detail with respect toFIG. 21 and embodiments discussed herein.

Network node 14 includes one or more communication interfaces 26 forcommunicating with one or more other network nodes 14, wireless device12, and/or other elements in system 10. In one or more embodiments,communication interface 26 includes one or more transmitters and/or oneor more receivers. Network node 14 includes processing circuitry 28.Processing circuitry 28 includes processor 30 and memory 32. In additionto a traditional processor and memory, processing circuitry 28 maycomprise integrated circuitry for processing and/or control, e.g., oneor more processors and/or processor cores and/or FPGAs (FieldProgrammable Gate Array) and/or ASICs (Application Specific IntegratedCircuitry). Processor 30 may be configured to access (e.g., write toand/or reading from) memory 32, which may comprise any kind of volatileand/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM(Random Access Memory) and/or ROM (Read-Only Memory) and/or opticalmemory and/or EPROM (Erasable Programmable Read-Only Memory). Suchmemory 32 may be configured to store code executable by processor 30and/or other data, e.g., data pertaining to communication, e.g.,configuration and/or address data of nodes, etc.

Processing circuitry 28 may be configured to control any of the methodsand/or processes described herein and/or to cause such methods and/orprocesses to be performed, e.g., by network node 14. Processor 30corresponds to one or more processors 30 for performing network node 14functions described herein. Network node 14 includes memory 32 that isconfigured to store data, programmatic software code and/or otherinformation described herein. In one or more embodiments, memory 32 isconfigured to store aggregation code 34. For example, aggregation code34 includes instructions that, when executed by processor 30, causesprocessor 30 to perform the process discussed in detail with respect toFIG. 17 and embodiments discussed herein.

FIG. 17 is a flow diagram of one exemplary embodiment of the aggregationprocess of aggregation code 34 in accordance with the principles of someembodiments of the disclosure. Processing circuitry 28 selects a firstset and second set of reference signal resources in a subframe, thefirst set and second set of reference signal resources satisfies atemporal criterion and a frequency criterion for separation betweenresource elements (Block S100). Processing circuitry 28 is furtherconfigured to aggregate the first set and second set of reference signalresources to the subframe to form a CDM aggregation configuration (BlockS102). In one or more embodiments, processing circuitry 28 communicatesCDM aggregation configuration to a wireless device 12.

In one or more embodiments (collectively referred to as Embodiment A),to minimize the risk of performance losses due to channel variationsacross OFDM symbols, some constraints are introduced on which pair oflegacy 8-port CSI-RS resources can be used to perform CDM-4 aggregation.The pair of legacy 8-port CSI-RS resources are chosen such that thelargest time separation between CSI-RS REs in the two legacy 8-portCSI-RS resources is limited to less than 6 OFDM symbols. For instance,the CSI-RS REs in legacy 8-port CSI-RS resources 0 and 2 have a maximumseparation of 6 OFDM symbols (i.e., referring to FIG. 11 , CSI-RS REs oflegacy 8-port CSI-RS resource 0 in OFDM symbol 5 of the first slot areseparated by 6 OFDM symbols from the CSI-RS REs of legacy 8-port CSI-RSresource 2 in OFDM symbol 3). This can help reduce the performancelosses due to channel variations in time, as this approach only requiresthe channel to be invariant over a maximum of 6 OFDM symbols to ensureorthogonality within the resulting CDM-8 groups. The list of allowedpairs of legacy 8-port CSI-RS resources over which CDM-4 aggregation canbe performed to obtain a CDM-8 group is given in Table 5 thatillustrates a list of 8-port CSI-RS configuration pairings for CDM-4aggregation.

TABLE 5 List of Allowed 8-port CSI-RS Configuration Pairings for CDM-4Aggregation CDM-4 Aggregation Pair of 8 port CSI-RS ConfigurationsConfigurations 0 0 1 1 0 2 2 0 3 3 1 2 4 1 3 5 1 4 6 2 3 7 2 4 8 3 4

Table 5 indicates the pair of 8-port CSI-RS configurations that can bein any order. For instance the pair (3,4) corresponding to the last rowof Table 5 applies to both the following cases:

-   -   The first 8-port CSI-RS configuration is 3 and the second 8-port        CSI-RS configuration is 4;    -   The first 8-port CSI-RS configuration is 4 and the second 8-port        CSI-RS configuration is 3.

The exact order of the 8-port CSI-RS configurations is determined by theCSI-RS resource number i defined in Equation 12. In some embodiments,one or more CDM-4 aggregation configuration indices (which representsthe pair of 8-port CSI-RS configurations) is signaled to the wirelessdevice by the network node via higher layer signaling.

An example of CDM-8 design using embodiment is given as follows. Thenetwork node configures the wireless device with 32 NZP CSI-RS ports byaggregating legacy 8-port CSI-RS resources in the order 4, 0, 2, 1 whereresource 4 corresponds to CSI-RS resource number i=0 and resource 1corresponds to CSI-RS resource number i=3 (note that CSI-RS resourcenumber i is defined as in Equation 12). As a next step, the network nodeforms CDM-8 groups by aggregating CDM-4 groups across the allowed pairsof legacy 8-port CSI-RS resources given in Table 5. For instance, thenetwork node can aggregate the CDM-4 groups across legacy 8-portresource pairs (2,4) and (0,1) which correspond to CDM-4 aggregationconfigurations 7 and 0 in Table 5. The resulting CDM-8 groups are shownin FIG. 18 . In FIG. 18 , CDM-8 groups indicated by A and B are a resultof aggregating CDM-4 groups across 8-port CSI-RS resources pairs (2,4);CDM-8 groups indicated by C and D are a result of aggregating CDM-4groups across 8-port CSI-RS resources pairs (0,1). Note that theresource elements of all 4 CDM-8 groups have a maximum time separationΔT=6 symbols, as highlighted in FIG. 18 for Group C. Furthermore, groupsare not formed from with configurations with maximum time separations ofΔT=9 symbols, as illustrated in example in FIG. 18 . In one or moreembodiments, network node 14 then indicates CDM-4 aggregationconfiguration indices 7 and 0 to wireless device 12 via higher layersignaling. The wireless device uses this signal to know the CDM-8 groupsbeing used for NZP CSI-RS transmission and performs channel estimation.

In one or more other embodiments (collectively referred to as EmbodimentB), according to the list of allowed 8-port CSI-RS configurationpairings in Table 5, the aggregation of CDM-4 groups across 8-portCSI-RS resource configurations 1 and 4 are allowed. However, if theCDM-4 aggregation across 8-port CSI-RS resource configurations 1 and 4are done as shown in FIG. 19 , where the CDM-4 aggregation or resultingCDM-8 group (denoted by CSI-RS REs with A) can suffer from channelvariations in the frequency domain. The two CDM-4 groups beingaggregated together in FIG. 19 are separated 8 subcarriers. In order forthe orthogonality of the CDM-8 group to hold, the channel needs to beinvariant over 8 subcarriers, and under deployment scenarios with highdelay spread, this condition is not easily met. Hence, in addition tominimizing the risk of performance losses due to channel variationsacross symbols (as done in Embodiment A), it is also important to limitthe performance losses due to channel variations in the frequency domain(i.e., across subcarriers).

In Embodiment A, additional constraints are introduced on which CDM-4groups within a pair of legacy 8-port resource configurations can beaggregated together. The two CDM-4 groups within a pair of legacy 8-portresource configurations being aggregated together are selected such thatfrequency separation between the two groups is no more than 6subcarriers. The 6 subcarrier maximum separation is selected here sincethe OCC length 4 code in the case of 12 port NZP CSI-RS designs of LTERelease 13 are also separated by 6 subcarriers (see FIG. 10 ). The listof allowed CDM-4 aggregations within pairs of legacy 8-port CSI-RSresources to obtain a CDM-8 group is given in Table 6.

TABLE 6 List of Allowed CDM-4 Aggregations within a pair of 8-portCSI-RS configurations 8 port CSI-RS Configuration and CDM-4 groupcombination pairs First 8-port Second 8-port CDM-4 CSI-RS CSI-RS SecondConfigurations resource First CDM-4 resource CDM-4 AggregationConfiguration Group Configuration Group 0 0 i 1 i 1 0 i 1 ii 2 0 ii 1 ii3 0 i 2 i 4 0 i 2 ii 5 0 ii 2 i 6 0 ii 2 ii 7 0 i 3 i 8 0 ii 3 i 9 0 ii3 ii 10 1 i 2 i 11 1 ii 2 i 12 1 ii 2 ii 13 1 i 3 i 14 1 ii 3 i 15 1 ii3 ii 16 1 i 4 i 17 1 ii 4 i 18 1 ii 4 ii 19 2 i 3 i 20 2 ii 3 i 21 2 ii3 ii 22 2 i 4 i 23 2 i 4 ii 24 2 ii 4 i 25 2 ii 4 ii 26 3 i 4 i 27 3 i 4ii 28 3 ii 4 ii

In Table 6, i and ii represent the first and second CDM-4 groups withina legacy 8-port CSI-RS resource respectively.

It should be noted that Table 6 indicates 8-port CSI-RS configurationand CDM-4 group combination pairs that can be in any order. For instancethe combination pairs (3,ii) and (4,ii) corresponding to the last row ofTable 6 applies to both the following cases:

-   -   The first 8-port CSI-RS configuration is 3 and the second 8-port        CSI-RS configuration is 4;    -   The first 8-port CSI-RS configuration is 4 and the second 8-port        CSI-RS configuration is 3.

The exact order of the 8-port CSI-RS configurations is determined by theCSI-RS resource number i defined in Equation 12. In some embodiments,one or more CDM-4 aggregation configuration indices (which representsthe 8 port CSI-RS Configuration and CDM-4 group combination pairs) issignaled to the wireless device by network node via higher layersignaling. In an alternate embodiment, only the 1^(st) CDM-4 groupsbetween pairs of 8-port CSI-RS configurations are allowed to beaggregated and similarly only the 2^(nd) CDM-4 groups between pairs of8-port CSI-RS configurations are allowed to be aggregated.

An alternative list of allowed CDM-4 aggregations within pairs of legacy8-port CSI-RS resources to obtain a CDM-8 group is given in Table 7.

TABLE 7 An Alternative List of Allowed CDM-4 Aggregations within a pairof 8-port CSI-RS configurations 8 port CSI-RS Configuration and CDM-4group combination pairs First 8-port Second 8-port CDM-4 CSI-RS CSI-RSSecond Configurations resource First CDM-4 resource CDM-4 AggregationConfiguration Group Configuration Group 0 0 i 1 i 1 0 ii 1 ii 2 0 i 2 i3 0 ii 2 ii 4 0 i 3 i 5 0 ii 3 ii 6 1 i 2 i 7 1 ii 2 i 8 1 ii 2 ii 9 1 i3 i 10 1 ii 3 i 11 1 ii 3 ii 12 1 i 4 i 13 1 ii 4 ii 14 2 i 3 i 15 2 ii3 i 16 2 ii 3 ii 17 2 i 4 i 18 2 ii 4 ii 19 3 i 4 i 20 3 ii 4 ii

In Table 7, only the 1^(st) CDM-4 groups between pairs of 8-port CSI-RSconfigurations are allowed to be aggregated and similarly only the2^(nd) CDM-4 groups between pairs of 8-port CSI-RS configurations areallowed to be aggregated with the exception of three rows (rows 7, 10and 15). The reason for choosing the combination pairs listed in rows 7,10, and 15 is that these combination pairs are located in the same twoOFDM symbols (i.e., OFDM symbols 2-3 in the second slot) and have amaximum frequency separation of 6 subcarriers.

In a further alternative embodiment, CDM-4 group aggregation within thesame 8-port CSI-RS configuration is also allowed. In some cases, CDM-4aggregation within the same 8-port CSI-RS configuration may be combinedwith CDM-4 aggregation across pairs of 8-port CSI-RS configurations. Anexample showing CDM-4 aggregation within 8-port CSI-RS resource combinedwith CDM-4 aggregation across a pair of 8-port CSI-RS resources in shownin FIG. 20 . In FIG. 20 , the CDM-8 group indicated by C is formed byCDM-4 group aggregation within the same 8-port CSI-RS configuration.

Antenna Port Numbering

For CSI reference signals transmitted on 24 and 32 antenna ports, theantenna ports will be p=15, . . . , 38 and p=15, . . . , 46respectively. When aggregating multiple legacy CSI-RS resources of 8ports to form a CSI-RS resource for 24 or 28 ports, mapping between eachantenna port to a CSI-RS RE needs to be defined in order for a wirelessdevice to measure the channel of each antenna port correctly. A numberof solutions by using 24 and 32 ports as examples are discussed below.

For CSI reference signals using 24 or 32 antenna ports, N_(res) ^(CSI)CSI-RS resource configurations in the same subframe, numbered from 0 toN_(res) ^(CSI)−1, are aggregated to obtain N_(res) ^(CSI)N_(ports)^(CSI) antenna ports in total. Each CSI-RS resource configuration insuch an aggregation corresponds to N_(ports) ^(CSI)=8 antenna ports andone of the CSI-RS configurations in Table 2. N_(res) ^(CSI) andN_(ports) ^(CSI) respectively denote the number of aggregated CSI-RSresources and the number of antenna ports per aggregated CSI-RS resourceconfiguration. The values of N_(res) ^(CSI) and N_(ports) ^(CSI) for thecases of 24 and 32 port NZP CSI-RS design are given in Table 8.

TABLE 8 Aggregation of CSI-RS configurations for 24 and 32 ports Numberof antenna Total number of ports per CSI-RS Number of CSI-RS antennaports configuration configurations N_(res) ^(CSI)N_(ports) ^(CSI)N_(ports) ^(CSI) N_(res) ^(CSI) 24 8 3 32 8 4

A solution by using 32 ports as an example is discussed, where a UE issignaled with a list of four 8 ports CSI-RS resources, i.e. {k₀, k₁, k₂,k₃} and k_(i)∈{0,1,2,3,4} is one of the 8 ports CSI-RS resourceconfigurations in Table 2. For the case of OCC8, i.e., when higher layerparameter ‘cdmType’ is set to cdm8, and a list of N_(res) ^(CSI)=4CSI-RS resource configurations {k₀, k₁, k₂, k₃}, the list is reorderedto a new list {m₀, m₁, m₂, m₃} such that m₀=k₀ and m₁ corresponds to thefirst entry in {k₁, k₂, k₃} that the pair of CSI-RS resources {m₀, m₁}meet the constraints discussed in Embodiment A Similarly, {m₂, m₃} arethe second pair of CSI-RS resources with m₃=k_(i) and m₄=k_(j)(i,j∈{1,2,3}) such that j>i;

The mapping of the reference signal sequence r_(l,n) _(s) (m) ofEquation 5 to the complex-valued modulation symbols a_(k,l) ^((p)) usedas reference symbols on antenna port p are defined as:

a_(k, l)^((p^(′))) = w_(p^(′))(i) ⋅ r_(l, n_(s))(m^(′)) where$k = {k_{q}^{\prime} + {12m} - \left\{ \begin{matrix}k^{''} & {{{{for}\ p^{\prime}} \in \left\{ {15,\ldots,22} \right\}},\ {{normal}{cyclic}\ {prefix}},{N_{ports}^{CSI} = 8}} \\{k^{''} + 6} & {{{{for}\ p^{\prime}} \in \left\{ {23,\ldots,30} \right\}},\ {{normal}{cyclic}\ {prefix}},{N_{ports}^{CSI} = 8}}\end{matrix} \right.}$ $l = {l_{q}^{\prime} + \left\{ \begin{matrix}l^{''} & {{{{CSI}{reference}{signal}{configurations}0} - 19},{{normal}{cyclic}{prefix}}} \\{2l^{''}} & {{{{CSI}{reference}{signal}{configurations}20} - 31},{{normal}{cyclic}{prefix}}}\end{matrix} \right.}$ q = 0, 1 l^(″) = 0, 1 k^(′′) = 0, 1i = 4q + 2k^(′′) + l^(′′) m m = 0, 1, …, N_(RB)^(DL) − 1$m^{\prime} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}$

and where w_(p′)(i) is given by Table 9.

TABLE 9 p′ [w_(p′)(0) w_(p′)(1) w_(p′)(2) w_(p′)(3) w_(p′)(4) w_(p′)(5)w_(p′)(6) w_(p′)(7)] 15, 23 [1 1 1 1 1 1 1 1] 16, 24 [1 −1 1 −1 1 −1 1−1] 19, 25 [1 1 −1 −1 1 1 −1 −1] 20, 26 [1 −1 −1 1 1 −1 −1 1] 15, 27 [11 1 1 −1 −1 −1 −1] 16, 28 [1 −1 1 −1 −1 1 −1 1] 19, 29 [1 1 −1 −1 −1 −11 1] 20, 30 [1 −1 −1 1 −1 1 1 −1]

The quantity (k_(q)′, l_(q)′) corresponds to (k′, l′) given in Table 2of a CSI-RS resource configuration n_(q) (q=0,1) and {n₀, n₁} is a pairof CSI-RS configurations used for CDM8. (n₀, n₁)=(m₀, m₁) or (n₀,n₁)=(m₂, m₃). The quantity (k′, l′) and the necessary conditions onn_(s) are given by Table 2. Let i be the ith pair of CSI-RS resources,i.e. (m_(2i), m_(2i+1)), the relation between the antenna port number pand the quantity P can be described asp=i2N _(ports) ^(CSI) +p′  Equation 14

where p′∈{15, 16, . . . 15+2N_(ports) ^(CSI)−1} for the ith pair ofCSI-RS resources (m_(2i), m_(2i+i)) and i∈{0,1}, N_(ports) ^(CSI)=8.

FIG. 21 is a flow diagram of one exemplary embodiment of the channelprocess of channel code 24 in accordance with the principles of thedisclosure. Processing circuitry 18 receives a CDM aggregationconfiguration corresponding to an aggregated first set and second set ofreference signal resources in a subframe, the first set and second setof reference signal resources satisfying a temporal criterion and afrequency criterion for separation between resource elements (BlockS104). The selected first set and second set of reference signalresources in the subframe configured to reduce performance losses due toat least one channel variation across a plurality of symbols in thesubframe. Processing circuitry 18 performs channel estimation based onthe CDM aggregation configuration (Block S106).

FIG. 22 shows an example of antenna port numbering with CDM8 and 32ports with {k₀, k₁, k₂, k₃}={0, 4, 1, 3}. To satisfy the constraintsdiscussed in Embodiment A, the CSI-RS resource configurations arere-ordered as {m₀, m₁, m₂, m₃}={0,1, 4, 3}. Then the first CSI-RSresource pair is {n₀, n₁}=(0,1) and the second pair is {n₀, n₁}=(4,3).For the first pair of resources {n₀, n₁}=(0,1), the CDM8 cover codew_(p′)(0), . . . , w_(p′)(3) are mapped to the CSI-RS REs of config 0while w_(p′()4), . . . , w_(p′)(7) are mapped to the CSI-RS REs ofconfig 1. Similarly, for the second pair of resources {n₀, n₁}=(4,3),the CDM8 cover code w_(p′)(0), . . . w_(p′)(3) are mapped to the CSI-RSREs of config 4 while w_(p′)(4), . . . , w_(p′)(7) are mapped to theCSI-RS REs of config 3. Note that the subscription p′ of w′_(p) isomitted in the figure for simplicity. The antenna port p can be derivedaccording to {m₀, m₁, m₂, m₃}={0,1, 4, 3} and, where the first 16 portsp={15, . . . , 30} are mapped to REs associated with the first CSI-RSresource pair {m₀, m₁}={0,1} and the next 16 ports p={31, . . . , 46}are mapped to REs associated with the second CSI-RS resource pair {m₂,m₃}={4,3}.

In one or more embodiments, network node 14 includes aggregationprocessing module. Aggregation processing module is configured to selecta first set and second set of reference signal resources in a subframe.The aggregation processing module is further configured to aggregate thefirst set and second set of reference signal resources to the subframeto form a code division multiplexing, CDM, aggregation configuration.The first set and second set of reference signal resources in thesubframe satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources in the subframe satisfy afrequency criterion such that any two resource elements in the first setand second set of reference signal resources have up to a maximumfrequency separation of six subcarriers.

In one or more embodiments, a wireless device 14 includes a channelprocessing module configured to receive a CDM aggregation configurationcorresponding to an aggregated first set and second set of referencesignal resources in a subframe. The CDM aggregation configurationconfigured to perform channel estimation based on the CDM aggregationconfiguration. The first set and second set of reference signalresources in the subframe satisfy a temporal criterion such that any tworesource elements in the first set and second set of reference signalresources have up to a maximum time separation of six OFDM symbols. Thefirst set and second set of reference signal resources in the subframesatisfy a frequency criterion such that any two resource elements in thefirst set and second set of reference signal resources have up to amaximum frequency separation of six subcarriers.

Some embodiments include:

Embodiment 1A. A network node 14, comprising:

processing circuitry 28 configured to:

-   -   select a first set and second set of reference signal resources        in a subframe to reduce performance losses due to at least one        channel variation across a plurality of symbols in the subframe;        and    -   communicate the selected first set and second set of reference        signal resources to a wireless device.

Embodiment 2A. The network node 14 of Embodiment 1A, wherein the atleast one channel variation across the plurality of symbols in thesubframe includes a channel variation in time.

Embodiment 3A. The network node 14 of any of Embodiments 1A-2A, whereinthe selection of the first set and second set of reference signalresources in the subframe satisfies a temporal criterion, the temporalcriterion defining a maximum time separation between any two symbols ofthe plurality of symbols to be six symbols.

Embodiment 4A. The network node 14 of any of Embodiments 1A-3A, whereinthe at least one channel variation across symbols includes a channelvariation in the frequency domain.

Embodiment 5A. The network node of any of Embodiments 1A-4A, wherein theselection of the first set and second set of reference signal resourcesin the subframe satisfies a frequency criterion, the frequency criteriondefining a maximum frequency separation between any two subcarrierscarrying the plurality of symbols to be six subcarriers.

Embodiment 6A. The network node 14 of any one of Embodiments 1A-5A,wherein the first set of reference signal resources corresponds to afirst reference signal configuration including a first portion of thereference signal resources;

the second set of reference signal resources corresponds to a secondportion of reference signal resources different from the first portionof reference signal resources.

Embodiment 7A. The network node 14 of Embodiment 6A, wherein the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration; and

the second reference signal configuration is at least a second CSI-RSconfiguration different from the at least first CSI-RS configuration.

Embodiment 8A. The network node 14 of any of Embodiments 1A-7A, whereinthe first set and second set of reference signal resources in thesubframe are aggregated to form a code division multiplexing, CDM,aggregation configuration.

Embodiment 9A. The network node of Embodiment 8A, wherein the first setof reference signal resources in the subframe includes a subset ofresource from an eight port CSI-RS resource;

the second set of reference signal resources in the subframe includes asubset of resources in a different eight port CSI-RS resource from theeight port CSI-RS resource in the first set of reference signalresources; and

the CDM aggregation configuration having an orthogonal code cover oflength eight.

Embodiment 10A. A method, comprising:

selecting a first set and second set of reference signal resources in asubframe to reduce performance losses due to at least one channelvariation across a plurality of symbols in the subframe; and

communicating the selected first set and second set of reference signalresources to a wireless device 12.

Embodiment 11A. The method of Embodiment 10A, wherein the at least onechannel variation across the plurality of symbols in the subframeincludes a channel variation in time.

Embodiment 12A. The method of any of Embodiments 10A-11A, wherein theselection of the first set and second set of reference signal resourcesin the subframe satisfies a temporal criterion, the temporal criteriondefining a maximum time separation between any two symbols of theplurality of symbols to be six symbols.

Embodiment 13A. The method of any of Embodiments 10A-12A, wherein the atleast one channel variation across symbols includes a channel variationin the frequency domain.

Embodiment 14A. The method of any of Embodiments 10A-13A, wherein theselection of the first set and second set of reference signal resourcesin the subframe satisfies a frequency criterion, the frequency criteriondefining a maximum frequency separation between any two carrierscarrying the plurality of symbols to be six subcarriers.

Embodiment 15A. The method of any one of Embodiments 10A-14A, whereinthe first set of reference signal resources corresponds to a firstreference signal configuration including a first portion of thereference signal resources;

the second set of reference signal resources corresponds to a secondportion of reference signal resources different from the first portionof reference signal resources.

Embodiment 16A. The method of Embodiment 15A, wherein the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration; and

the second reference signal configuration is at least a second CSI-RSconfiguration different from the at least first CSI-RS configuration.

Embodiment 17A. The method of any of Embodiments 10A-16A, wherein thefirst set and second set of reference signal resources in the subframeare aggregated to form a code division multiplexing, CDM, aggregationconfiguration.

Embodiment 18A. The method of Embodiment 17A, wherein the first set ofreference signal resources in the subframe includes a subset ofresources within an eight port CSI-RS resource;

the second set of reference signal resources in the subframe includes asubset of resources within a different eight port CSI-RS resource fromthe eight port CSI-RS resource in the first set of reference signalresources; and

the CDM aggregation configuration having an orthogonal code cover oflength eight.

Embodiment 19A. A wireless device 12, comprising:

processing circuitry 18 configured to:

-   -   receive an indication of a selected first set and second set of        reference signal resources in a subframe, the selected first set        and second set of reference signal resources in the subframe        configured to reduce performance losses due to at least one        channel variation across a plurality of symbols in the subframe;    -   perform channel estimation based on the selected first set and        second set of reference signal resources in the subframe.

Embodiment 20A. The wireless device 12 of Embodiment 19A, wherein the atleast one channel variation across the plurality of symbols in thesubframe includes a channel variation in time.

Embodiment 21A. The wireless device 12 of any of Embodiments 19A-20A,wherein the first set and second set of reference signal resources inthe subframe satisfies a temporal criterion, the temporal criteriondefining a maximum time separation between any two symbols of theplurality of symbols to be six symbols.

Embodiment 22A. The wireless device 12 of any of Embodiments 19A-21A,wherein the at least one channel variation across symbols includes achannel variation in the frequency domain.

Embodiment 23A. The wireless device 12 of any of Embodiments 19A-22A,wherein the first set and second set of reference signal resources inthe subframe satisfies a frequency criterion, the frequency criteriondefining a maximum frequency separation between any two carrierscarrying the plurality of symbols to be six subcarriers.

Embodiment 24A. The wireless device 12 of any one of Embodiments19A-23A, wherein the first set of reference signal resources correspondsto a first reference signal configuration including a first portion ofthe reference signal resources;

the second set of reference signal resources corresponds to a secondportion of reference signal resources different from the first portionof reference signal resources.

Embodiment 25A. The wireless device 12 of Embodiment 24A, wherein thefirst reference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration; and

the second reference signal configuration is at least a second CSI-RSconfiguration different from the at least first CSI-RS configuration.

Embodiment 26A. The wireless device 12 of any of Embodiments 19A-25A,wherein the first set and second set of reference signal resources inthe subframe are aggregated to form a code division multiplexing, CDM,aggregation configuration.

Embodiment 27A. The wireless device 12 of Embodiment 26A, wherein thefirst set of reference signal resources in the subframe includes asubset of resources within an eight port CSI-RS resource;

the second set of reference signal resources in the subframe includes asubset of resources within a different eight port CSI-RS resource fromthe eight port CSI-RS resources in the first set of reference signalresources; and

the CDM aggregation configuration having an orthogonal code cover oflength eight.

Embodiment 28A. The wireless device 12 of any of Embodiments 19A-27A,wherein the processing circuitry 18 is further configured to map theselected first set and second set of reference signal resources in thesubframe to a plurality of antenna ports.

Embodiment 29A. A method, comprising:

receiving an indication of a selected first set and second set ofreference signal resources in a subframe, the selected first set andsecond set of reference signal resources in the subframe configured toreduce performance losses due to at least one channel variation across aplurality of symbols in the subframe;

performing channel estimation based on the selected first set and secondset of reference signal resources in the subframe.

Embodiment 30A. The method of Embodiment 29A, wherein the at least onechannel variation across the plurality of symbols in the subframeincludes a channel variation in time.

Embodiment 31A. The method of any of Embodiments 29A-30A, wherein thefirst set and second set of reference signal resources in the subframesatisfies a temporal criterion, the temporal criterion defining amaximum time separation between any two symbols of the plurality ofsymbols to be six symbols.

Embodiment 32A. The method of any of Embodiments 29A-31A, wherein the atleast one channel variation across symbols includes a channel variationin the frequency domain.

Embodiment 33A. The method of any of Embodiments 29A-32A, wherein thefirst set and second set of reference signal resources in the subframesatisfies a frequency criterion, the frequency criterion defining amaximum frequency separation between any two subcarriers carrying theplurality of symbols to be six subcarriers.

Embodiment 34A. The method of any one of Embodiments 29A-33A, whereinthe first set of reference signal resources corresponds to a firstreference signal configuration including a first portion of thereference signal resources;

the second set of reference signal resources corresponds to a secondportion of reference signal resources different from the first portionof reference signal resources.

Embodiment 35A. The method of Embodiment 34A, wherein the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration; and

the second reference signal configuration is at least a second CSI-RSconfiguration different from the at least first CSI-RS configuration.

Embodiment 36A. The method of any of Embodiments 29A-35A, wherein thefirst set and second set of reference signal resources in the subframeare aggregated to form a code division multiplexing, CDM, aggregationconfiguration.

Embodiment 37A. The method of Embodiment 36A, wherein the first set ofreference signal resources in the subframe includes a subset ofresources within an eight port CSI-RS resource;

the second set of reference signal resources in the subframe includes asubset of resources within a different eight port CSI-RS resource fromthe eight port CSI-RS resource in the first set of reference signalresources; and

the CDM aggregation configuration having an orthogonal code cover oflength eight.

Embodiment 38A. The method of any of Embodiments 29A-37A, wherein theprocessing circuitry is further configured to map the selected first setand second set of reference signal resources in the subframe to aplurality of antenna ports.

Embodiment 39A. A network node 14, comprising:

an aggregation processing module configured to:

-   -   select a first set and second set of reference signal resources        in a subframe to reduce performance losses due to at least one        channel variation across a plurality of symbols in the subframe;        and    -   communicate the selected first set and second set of reference        signal resources to a wireless device 12.

Embodiment 40A. A wireless device 12, comprising:

channel processing module configured to:

-   -   receive an indication of a selected first set and second set of        reference signal resources in a subframe, the selected first set        and second set of reference signal resources in the subframe        configured to reduce performance losses due to at least one        channel variation across a plurality of symbols in the subframe;    -   perform channel estimation based on the selected first set and        second set of reference signal resources in the subframe.

Some Other Embodiments

According to one aspect of the disclosure, a network node 14 isprovided. The network node includes processing circuitry 18 configuredto: select a first set and second set of reference signal resources in asubframe and aggregate the first set and second set of reference signalresources in the subframe to form a code division multiplexing, CDM,aggregation configuration. The first set and second set of referencesignal resources in the subframe satisfy a temporal criterion such thatany two resource elements in the first set and second set of referencesignal resources have up to a maximum time separation of six OFDMsymbols. The first set and second set of reference signal resources inthe subframe satisfy a frequency criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration.

According to one embodiment of this aspect, the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration. The second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources. The CDM aggregation configuration has anorthogonal cover code of length eight. According to one embodiment ofthis aspect, the processing circuitry 28 is further configured tocommunicate the CDM aggregation configuration to a wireless device 12.According to one embodiment of this aspect, the CDM aggregationconfiguration is an aggregation of two CDM-4 groups.

According to another aspect of the disclosure, a method is provided. Afirst set and second set of reference signal resources in a subframe areselected. The first set and second set of reference signal resources areaggregated to the subframe to form a code division multiplexing, CDM,aggregation configuration. The first set and second set of referencesignal resources in the subframe satisfy a temporal criterion such thatany two resource elements in the first set and second set of referencesignal resources have up to a maximum time separation of six OFDMsymbols. The first set and second set of reference signal resources inthe subframe satisfy a frequency criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum frequency separation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration. According to oneembodiment of this aspect, the first set of reference signal resourcesin the subframe includes a subset of resources from an eight port CSI-RSresource configuration. The second set of reference signal resources inthe subframe includes a subset of resources in a different eight portCSI-RS resource configuration different from the eight port CSI-RSresource configuration corresponding to the first set of referencesignal resources. The CDM aggregation configuration having an orthogonalcover code of length eight.

According to one embodiment of this aspect, the CDM aggregationconfiguration is communicated to a wireless device 12. According to oneembodiment of this aspect, the CDM aggregation configuration is anaggregation of two CDM-4 groups.

According to another aspect of the disclosure, a wireless device 12 isprovided. The wireless device includes processing circuitry 28configured to receive a CDM aggregation configuration corresponding toan aggregated first set and second set of reference signal resources ina subframe and perform channel estimation based on the CDM aggregationconfiguration. The first set and second set of reference signalresources satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources satisfy a frequencycriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum frequencyseparation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration.

According to one embodiment of this aspect, the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration. The second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources. The CDM aggregation configuration havingan orthogonal cover code of length eight. According to one embodiment ofthis aspect, the processing circuitry 28 is further configured to mapthe selected first set and second set of reference signal resources inthe subframe to a plurality of antenna ports. According to oneembodiment of this aspect, the CDM aggregation configuration is anaggregation of two CDM-4 groups.

According to another aspect of the disclosure, a method for a wirelessdevice 12 is provided. A CDM aggregation configuration corresponding toan aggregated first set and second set of reference signal resources ina subframe is received. The first set and second set of reference signalresources. Channel estimation is performed based on the CDM aggregationconfiguration. The first set and second set of reference signalresources satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources satisfy a frequencycriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum frequencyseparation of six subcarriers.

According to one embodiment of this aspect, the first set of referencesignal resources corresponds to a first portion of a first referencesignal configuration. The second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration. According to one embodiment of this aspect, the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration. The secondreference signal configuration is at least a second CSI-RS configurationdifferent from the at least first CSI-RS configuration.

According to one embodiment of this aspect, the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration. The second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources. The CDM aggregation configuration has anorthogonal cover code of length eight.

According to one embodiment of this aspect, the CDM aggregationconfiguration is an aggregation of two CDM-4 groups. According to oneembodiment of this aspect, the selected first set and second set ofreference signal resources in the subframe are mapped to a plurality ofantenna ports.

According to another aspect of the disclosure, a network node 14 isprovided. The network node 14 includes an aggregation processing moduleconfigured to: select a first set and second set of reference signalresources in a subframe and aggregate the first set and second set ofreference signal resources to the subframe to form a code divisionmultiplexing, CDM, aggregation configuration. The first set and secondset of reference signal resources in the subframe satisfy a temporalcriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum timeseparation of six OFDM symbols. The first set and second set ofreference signal resources in the subframe satisfy a frequency criterionsuch that any two resource elements in the first set and second set ofreference signal resources have up to a maximum frequency separation ofsix subcarriers.

According to one aspect of the disclosure, a wireless device 12 isprovided. The wireless device 12 includes a channel processing moduleconfigured to: receive a CDM aggregation configuration corresponding toan aggregated first set and second set of reference signal resources ina subframe, and perform channel estimation based on the CDM aggregationconfiguration. The first set and second set of reference signalresources satisfy a temporal criterion such that any two resourceelements in the first set and second set of reference signal resourceshave up to a maximum time separation of six OFDM symbols. The first setand second set of reference signal resources satisfy a frequencycriterion such that any two resource elements in the first set andsecond set of reference signal resources have up to a maximum frequencyseparation of six subcarriers.

According to one embodiment of this aspect, the channel processingmodule is further configured to communicate the CDM aggregationconfiguration to a wireless device. According to one embodiment of thisaspect, the CDM aggregation configuration is communicated to a wirelessdevice 12.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, the concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.”Furthermore, the disclosure may take the form of a computer programproduct on a tangible computer usable storage medium having computerprogram code embodied in the medium that can be executed by a computer.Any suitable tangible computer readable medium may be utilized includinghard disks, CD-ROMs, electronic storage devices, optical storagedevices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings which arelimited only by the following claims.

What is claimed is:
 1. A wireless device, comprising: processingcircuitry configured to: receive a code division multiplexing, CDM,aggregation configuration for a CDM-8 design for a plurality of CSI-RS,Channel System Information-Reference Signal, antenna ports, the CDMaggregation configuration corresponding to an aggregated first set andsecond set of reference signal resources in a subframe, the CDMaggregation configuration being an aggregation of two CDM-4 orthogonalcover codes, the two CDM-4 orthogonal cover codes being selected from aconstrained set of pairs that are selected to minimize loss oforthogonality of a length 8 cover code; perform channel estimation basedon the CDM aggregation configuration; the first set and second set ofreference signal resources satisfying a temporal criterion such that anytwo resource elements in the first set and second set of referencesignal resources have up to a maximum time separation of six OFDMsymbols; and the first set and second set of reference signal resourcessatisfy a frequency criterion such that any two resource elements in thefirst set and second set of reference signal resources have up to amaximum frequency separation of six subcarriers.
 2. The wireless deviceof claim 1, wherein the first set of reference signal resourcescorresponds to a first portion of a first reference signalconfiguration; and the second set of reference signal resourcescorresponds to a second portion of a second reference signalconfiguration.
 3. The wireless device of claim 2, wherein the firstreference signal configuration is at least a first channel stateinformation-reference signal, CSI-RS, configuration; and the secondreference signal configuration is at least a second CSI-RS configurationthat is different from the at least first CSI-RS configuration.
 4. Thewireless device of claim 3, wherein the first set of reference signalresources in the subframe includes a subset of resources from an eightport CSI-RS resource configuration; the second set of reference signalresources in the subframe includes a subset of resources in a differenteight port CSI-RS resource configuration different from the eight portCSI-RS resource configuration corresponding to the first set ofreference signal resources; and the CDM aggregation configuration has anorthogonal cover code of length eight.
 5. The wireless device of claim1, wherein the first set of reference signal resources in the subframeincludes a subset of resources from an eight port CSI-RS resourceconfiguration; the second set of reference signal resources in thesubframe includes a subset of resources in a different eight port CSI-RSresource configuration different from the eight port CSI-RS resourceconfiguration corresponding to the first set of reference signalresources; and the CDM aggregation configuration having an orthogonalcover code of length eight.
 6. The wireless device of claim 5, whereinthe processing circuitry is further configured to map the selected firstset and second set of reference signal resources in the subframe to aplurality of antenna ports.
 7. The wireless device of claim 1, whereinthe processing circuitry is further configured to map the selected firstset and second set of reference signal resources in the subframe to aplurality of antenna ports.
 8. The wireless device of claim 1, whereinthere are at least 24 CSI-RS, antenna ports.
 9. A method for a wirelessdevice, the method comprising: receiving a code division multiplexing,CDM, aggregation configuration for a CDM-8 design for a plurality ofCSI-RS, Channel System Information-Reference Signal, antenna ports, theCDM aggregation configuration corresponding to an aggregated first setand second set of reference signal resources in a subframe, the firstset and second set of reference signal resources, the CDM aggregationconfiguration being an aggregation of two CDM-4 orthogonal cover codes,the two CDM-4 orthogonal cover codes being selected from a constrainedset of pairs that are selected to minimize loss of orthogonality of alength 8 cover code; performing channel estimation based on the CDMaggregation configuration; the first set and second set of referencesignal resources satisfying a temporal criterion such that any tworesource elements in the first set and second set of reference signalresources have up to a maximum time separation of six OFDM symbols; andthe first set and second set of reference signal resources satisfying afrequency criterion such that any two resource elements in the first setand second set of reference signal resources have up to a maximumfrequency separation of six subcarriers.
 10. The method of claim 9,wherein the first set of reference signal resources corresponds to afirst portion of a first reference signal configuration; and the secondset of reference signal resources corresponds to a second portion of asecond reference signal configuration.
 11. The method of claim 10,wherein the first reference signal configuration is at least a firstchannel state information-reference signal, CSI-RS, configuration; andthe second reference signal configuration is at least a second CSI-RSconfiguration that is different from the at least first CSI-RSconfiguration.
 12. The method of claim 11, wherein the first set ofreference signal resources in the subframe includes a subset ofresources from an eight port CSI-RS resource configuration; the secondset of reference signal resources in the subframe includes a subset ofresources in a different eight port CSI-RS resource configurationdifferent from the eight port CSI-RS resource configurationcorresponding to the first set of reference signal resources; and theCDM aggregation configuration has an orthogonal cover code of lengtheight.
 13. The method of claim 9, wherein the first set of referencesignal resources in the subframe includes a subset of resources from aneight port CSI-RS resource configuration; the second set of referencesignal resources in the subframe includes a subset of resources in adifferent eight port CSI-RS resource configuration different from theeight port CSI-RS resource configuration corresponding to the first setof reference signal resources; and the CDM aggregation configurationhaving an orthogonal cover code of length eight.
 14. The method of claim13, further comprising mapping the selected first set and second set ofreference signal resources in the subframe to a plurality of antennaports.
 15. The method of claim 9, further comprising mapping theselected first set and second set of reference signal resources in thesubframe to a plurality of antenna ports.
 16. The wireless device ofclaim 9, wherein there are at least 24 CSI-RS, antenna ports.